USING-COMPUTED-HINTS-5

We have found that it is sometimes helpful to define hints so that
they print out messages to the terminal when they fire, so you can
see what hint was generated and which of your computed hints did it.

To that end we have defined a macro we sometimes use. Suppose you
have a :hints specification such as:

:hints (computed-hint-fn (hint-expr id))

If you defmacro the macro below you could then write instead:

:hints ((show-hint computed-hint-fn 1)
(show-hint (hint-expr id) 2))

with the effect that whenever either hint is fired (i.e., returns
non-nil), a message identifying the hint by the marker (1 or 2,
above) and the non-nil value is printed.

Note that when show-hint is applied to a hint that is a symbol,
e.g., computed-hint-fn, it applies the symbol to the four
computed-hint arguments: id, clause, world, and
stable-under-simplificationp. If computed-hint-fn is of
arity 3 the code above would cause an error. One way to avoid it
is to write

If you only use computed hints of arity 3, you might eliminate
the occurrence of stable-under-simplificationp in the definition
of show-hint above.

Putting a show-hint around a common hint has no effect. If you
find yourself using this utility let us know and we'll consider
putting it into the system itself. But it does illustrate that you
can use computed hints to do unusual things.